The present invention relates to the field of infrared remote control transmitters.
Infrared remote control systems for television receivers and the like are more desirable than more conventional ultrasonic remote control systems since they are significantly less susceptible to interference signals such as those stemming from multipath signal reflections. Unfortunately, the human eye may be harmed under conditions of prolonged, continuous and direct exposure to infrared (IR) radiation.
To reduce the possibility of harm to the eyes of users, special pulse codes are utilized in IR remote control systems to limit the duty cycle of IR radiation during the transmission of remote control messages. In addition, amplitude regulator circuits may be employed in remote control transmitters to maintain the power level of IR radiation during transmission under normal operating conditions. However, these precautions do not contemplate many component failure conditions which may cause excessive IR radiation.
In copending U.S. Pat. application Ser. No. 025,165 filed in the name of Dursun Sakarya on Mar. 29, 1979, a drive circuit for IR light-emitting diodes of a remote control transmitter is described which is arranged to be "fail-safe" in the sense that failures of components within the drive circuit result in the reduction of the amplitude of the drive signal and thereby the level of IR radiation during transmission.